Electronic switching means



July 28, 1959 F. H. RAYMOND ETAL 2,897,359

ELECTRONIC swrrcHING MEANS Fiiex ot. e. 1954 l v 2 sheets-sheet 1 July 28,1959 H. RAYMOND EEAL 2,897,359

ELECTRONIC SWITCHING MEANS Filed oct. e. 1954 2 'sheets-sheet 2 Arron/fn States ELECTRONIC SWITCHING Francois HenriV Raymond, SaintiGermain-en-Laye, andi` Monique Berthe Lilainand, Paris, France, assignors to Societe @Electronique et dAntomatisme, Courbevoie, France Application October 6, 1954, Serial No. 460,722'

Claims. priority, application France November 28, 1953 22 Claims. (Cl'. Z50-27) transmission path whenever the diode element is non-conl ducting or blocked; however, when the diode is conducting, a biasing voltage is. applied to that point of the transmission.. path so that, if this biasing voltage is properly calibrated with respect to the electric signal or voltage in the transmission path, only a residual voltage or signal isy left in this path for further transmission from that branchingv point. WhenY the transmitted signal forinstance consists of a uctuating amplitude. D;C. voltage, this residual voltage will consist at this point of voltage fluctuations on each side. of the biasing voltage, with the reduced` value being determined by the transfer characteristic presented by the-diode element itself.

This kind of electronic switch can be controlled in either one of the two following manners:

Externally, whereby the biasing voltage is switched over from one value for which the diode element is blocked, to another value for which the diode element is made conducting. These values are determined` with respect to the amplitude value of the electric voltage or signal the transmission of which is to be controlled by the switch, namely, the two values of the biasing voltages are selected on either side of the value or range of variations in amplitude of the electric voltage or signal.

Alternatively, switching is controlled 'by the amplitude change of the signal itself, the biasing voltage being fixed and selected at a predetermined value within the range of variation of the general voltage level.

Usually such an electronic switch is inserted in a transmission path by inserting in this path a series resistance attenuator and connecting a selected intermediate point of this attenuator to the diode element.

This kind of electronic switch includes a series resistance which at one end or terminal receives an applied signal. The suitably alternated signal is derived from the other end or terminal of the attenuator.

A diode element is connected at one of its electrodes to an intermediate point of the attenuator, and at its other electrode to a biasing point.

The terminal at the output end of the attenuator is normally connected to the input of a high gain amplifierl `atent the kind specified: used with or in analogue computation devices.

For such uses, the residual voltage. must be made substantially zero or, at least, easily.l to be compensated by means` of afixed compensating voltage of opposite polarity which may be. introduced either at the. output end 0r at any intermediate. point of" the attenuator. Ingeneral this will not` be` the case with known electronic switches of the kind specied. The fluctuations of the. residual voltage, when the switch operates. on amplitude. uctuating D.C.r signals, for instance, remaintoo wide to make possible. such cancellation or c ompensation inthe conducting periodsV of thediode element of such known switching apparatus. v

One object 0f the invention, therefore, isto provide an improvementin electronic switches of the kind speci-l tied permitting a residual voltage to be. obtained which is substantially zero,.orat least easily to; be compensated..

Further, accordingr to the invention, thererisprovided in an electronic; switch of the kind specilied, at least a second diode element connected at one, ofits electrodes to a secondpoint of` the resistancel attenuator. This second point of connection is located below the'firstone when looking in the. direction of transmission. The other electrode. of the second. diode is connected( to a second biasing point, the control arrangement being such that both diode elements are controlled substantiallyA simul-Y taneouslyI and the. voltage passed through thesecond ele.` ment, when conducting, is` adjusted to oppose the, at`

tenuated residual voltage, from the. rst element at its4 own point of connection, in suc-ha manner that the iinat residual output voltage from the attenuator is. substan-V tially zero or, at least, of such a narrow width of Vihctua'- tionY range that it. Ina-y be considered as compensatedr when opposed to a fixed compensating voltage4 thereat,l or at a point.- below the point of connection of theA second'v diode element.

A more specific. object of the invention is to combinel an electronic switch of thet kind specied with at' least one second diode element connected at one of-itselecifl trodes to a point of connection betweenv the point'of connection ofthe first. `diode, and thev output; end of the attenuator, the second diode. element; having its: other electrode connected. to a biasing point, and' the. biasing voltages beingv such-that the diodeelements are;controlled'A substantially simultaneously from and to their conducting states, and when the diode elements arerconductingY the second diode element operates toV so reduce the iluc`r Fig. l shows one form ofv an electronic switch ofthe kindv specied, togetherwith a high' gain negative feed` backampliier therefor;` Y

Figs. 2 and 4 represent two embodiments of electronic switching apparatus according to the invention;

Figs. 3 and 5 are graphs explaining certain operational features .ofthe invention; l

Fig. 6 illustrates-an. electronicY control arrangement for f an electronicswitch of thev kind4 shown in Fig. 2;

lFig. 7 illustrates ananalogue. device including two electronic switches ofthe kind shownin Fig. 4.

An electronic switch ofthe kind specified is shown in Fig. l and comprises, between the terminals 1 and 2, a

seriesl resistancev attenuator consisting of 2 serially con- Y nected resistors 3 and 4. Junction point 5 of these resistors is connected to the anode of diode 6, the cathode of which is connected to a terminal 7.

Terminal 7 is shown to be connected to the armature of a change-over contact receiving at 8 a voltage U1 and at 9 another voltage U2. Normally, the practical realization of such a changeaover contact will be a switch of the electronic type, as will be described further below, with reference to Figs. 6 and 7.

According to Fig. 1, a high gain D.C. amplier lil has its input connected to terminal 2 and is provided with a negative feedback impedance 11 extending from its output 12 to terminal 2. At 13 there is shown a multiplexing arrow to indicate that several additional attenuators may be connected, if desired, to terminal 2, and in this case amplifier 10 will operate to sum up the voltages brought to its input from all such attenuators. in case impedance 11 consists of a resistance, the signal derived at 12 will reproduce the overall input signal. In case impedance 11 consists of a capacity, the derived signal will be proportional to the integral value of this overall input signal; and so forth. It is however understood that the improvements on the electronic switch in accordance with the invention are by no means dependant upon the nature of the amplifier or any other circuit to which output terminal 2 of the switch is connected.

In considering Figs. 3 and 5 the input voltage E of the attenuator is assumed to be an amplitude varying D.C. signal with a range of variations between two possible values Em and EM, which may be on each side of the zero point, as in Fig. 3, or on one side only of this point, as in Fig. 5. In the right-hand portion of Figs. 3 and 5 the voltages are shown as seen from point 5.

When the voltage at point 7 is U2, the diode 6 is not conducting as this value U2 is higher than the maximum value EM seen from point 5. On the other hand when, the voltage at point 7 is at its value U1, which is lower than EM by an arbitrary interval or spacing a, diode 6 becomes conducting. At point 5 there results a residual voltage U which can vary between limits dened by the projections on the abscissa axis of the intersection points A and B of the respective load characteristics of diode 6 corresponding to signal values Em and EM, with the transfer characteristic proper of this diode 6. These projection points, C and D, dene a range of fluctuation Au of the residual voltage at point 5.

In spite of the attenuation due to resistance 3, the range AE of the input signal, as seen from point 5, cannot be so reduced that the residual range of variation Au itself is so small that a compensation voltage of constant value and of a polarity opposite to that of the residual voltage could be set, at a point of the attenuator. This will be desirable especially in analogue computation circuits wherein a high accuracy of results is required.

In accordance with the invention such as illustrated in F1g. 2, a further resistance 14 is inserted between resistances 3 and 4-with suitable redimensioning of these three. resistors to a predetermined attenuation value. Junction point 15 of resistances 14 and 4 is connected to an electrode of a second diode element, for instance to the anode of a diode 16, Fig. 2. Furthermore the cathode of diode 16, at point 17, is connected to a further inverter or changeover contact, such that when voltage U2 1s applied to the cathode of diode 6 it is also applied to the cathode of diode 16 and, when the voltage U1 is applied to the cathode of diode 6, there is applied to the cathode of diode 16 a voltage V1 of such a value as toI render diode 16 conducting substantially simultaneously with diode 6. Under these circumstances the overall operatlon of the electronic switch remains unchanged when both diodes are conducting, even if instead of voltage U2- a dnerent voltage V2 is applied to the cathode of diode 16, V2 being of a higher value than the signal voltage corresponding to EM, as seen from the terminal 15;

The overall operation, however, is modied as follows when both diodes are conducting: At point 5 a residual voltage appears with a variation range of Au, see righthand portion of Fig. 3. This residual voltage is attenuated through 14, and it is this attenuated voltage which then occurs at point 15. Since however the diode 16 presents a cathode biasing voltage of V1, spaced apart along the abscissa axis from bias voltage U1 of diode 6 by b, and if both transfer characteristics d1 and d2 of the diodes are considered as substantially identical and having the same slopes of load characteristics, a further residual voltage appears at point 15, and the range of variation Au is determined by the projection points H and I of the two intersection points F and G of curve d2 with the load characteristics from points C and D, the limit values of the former range of variation Au. It is apparent that the residual voltage range, Av, is narrower than the range Au. This reduction will depend, firstly, on the value of resistance 14- and, secondly, on the spacing a-i-b with respect to the former spacing a, i.e. the reduction will depend on the choice of V1 with respect to U1. Obviously, the graph does not take into account the attenuation introduced by 14 so that V1 appears more negative than U1 while the reverse is true in actual practice. Spacings A and a-i-b may be considered as plotted with respect to ditferent values of EM-Em, as seen from the point 5, for a, and from point 15, for b. At 15, the difference is C-D.

It will be noted that the range of variation Av can thus be obtained at such reduced value, considering the control voltages of the two diodes and the attenuation characteristics of the network, that a compensating voltage of the mean value of Av but of opposite polarity, may be introduced at will for substantially cancelling the residual voltage, as seen from output terminal 2.

As an alternative, the second diode can be provided with a direction of conduction reversed with respect to that of the first diode. This is shown in Fig. 4, wherein second diode 26 has its cathode connected to point 15 of the attenuator and its anode connected to a xed bias, for instance the earth potential. In Figs. 4 and 5 there is considered the case wherein signal input E can only vary within a range of positive values, as apparent from the graph of Fig. 5 which generally may be interpreted in a similar manner as Fig. 3.

The characteristic curve d2 of diode 16 in the graph of Fig. 3. In actual practice U1 is normally of negative value. With the arrangement of Fig. 4 when diode 6 is conducting, the positive signal voltage at 5 is converted into a negative residual voltage and transferred to point 15 with an attenuation due to resistance 14, and it is this negative residual value which makes diode 26 conducting and carries the earth potential to point 15.

Generally, a single additional diode will suice practically to provide an improved switch according to the invention, but it is apparent that the arrangement could be repeated, and, if required, one or several further diodes can be connected along the resistance attenuator, all these diodes being controlled substantially simultaneously with respect to their conducting and non-conducting states.

In case lan electronic switch according to the invention is used for the purpose of limiting a varying signal voltyage only, all control means separate from the electronic switch may be omitted and suitable bias voltages of constant values are then applied to both diode electrodes not connected to the attenuator. The incoming signal will be transmitted up or down to a critical value for which the irst diode becomes conducting. At the same time the second diode is also brought to its conducting state, and in this condition the output voltage from the -attenuator will be determined by the selected potential value of the bias applied to the second diode element.

On the other hand, in case the switch will have to be externally controlled through a change-over of the voltages applied .to its diode elements, or at least on the first diode in the direction of transmission of the attenuator,

senseo s uch a .changeover .is advantageously achieved through purely .electronic means. The diagrams of Pigs. 6 ,and 7 illustrate "two such electronic change'over controls for arrangements corresponding to those of Figs. 2 and 4 respectively.

lin Figs. 6 and 7 there are further developed certain anxiliary features which may be embodied in electronic switches according .to the invention.

Referring vto Fig. v6, the cathode of diode 6 is connected through the conductor or lead 19 to the cathode of a vacuum -tube 21 which is a triode cathode follower tllbe. Cathode load resistance 20 of tube 21 is negatively ybiased ,to v alue -Ul and the plate 2 2 of tube 21 is positively biased to value {U2. When this cathode follower `tube 21 is non-conducting, voltage U1 will be supplied to lead 19, and when tube 21 is conducting, lead 19 will receive voltage U2. .Obviously these terms U1 and U2 are to be interpreted in terms -of the actual voltages which must be present on the cathode of diode 6.

a similar way, the ,cathode .of the second vdiode 16 is connected through a lead 19 to the cathode of a second cathode follower .tube 31. The negative bias `of the cathode ,tube 3, through resistance 30, is .of a value V1,

and its high voltage plate supply is of the ,above men- 2 5 of any classical design, as for example more fully f disclosed in Fig. 7. Y

Trigger stage k2S is controlled from the relative potentiall conditions of its inputs 27 and 2S to its control grids. `One of the plate outputs of stage 25 is connected through series resistors 24 and 34, vto the -control .grids of the cathode follower tubes 21 Iand 31. -At V29, there is shown the plate resistance of the corresponding outpt ttpf trigger` stage 25. Negative bias rsistances 23 and 3 3 are shown for the respective control grids of the ttlbes 21 and 3 1. These controlgrids receive .each vtheir potentials from a voltage divider, and their tubes will lbe conducting when no .other current is drawn from .the voltage .dividers and non-conducting .when another cur.- rent '(e.g. through the corresponding tube of the trigger stage) exists. s

In case the cathode follower tubes are blocked,V vo1tages U1 and V1 respectively are applied .to the cathodes .of diodes 6 and 16, and these diodes conduct. Curtents are then established through resistances 20 and 30 and these lcurrents fluctuate in relation to the jiluctu- Y lins fof the residual voltages at points 5 and 15. Qonsequently voltages U1 and V1 will fluctuate yand .the characteristic curves d1 and d2, Fig. 3, will also fluctuate on either side of their positions shown.

In order -to .eliminate such fluctuations and to increase the `accuracy of compensation o f residual voltage pf the switch, .auxiliary compensation is provided; In this case incoming signal E is applied to the cathodes ,of tubes 21 and 31 with a polarity opposite .to that applied to input terminal 1, and with an amplitude suitably reduced to compensate for the fluctuations of potential across resistances 20 and 3 0. As illustrated in Fig. 6, a terminal 37 receives voltage -kpli and transmits this signal portion to the cathode of tube 21 through va `resistane 3 6; a terminal i7 receives voltage -k2.E and transmits this signal portion to the cathode vof tube 31 throngh a resistance 4 6.

Such auxiliary compensation may also be used V.in switches `of the type shown in Fig. 4. It will be apparent that the signal components applied to the diodes will not have any unblocking effect when the diodes are 6 blocked if value U2 is s o selected as to avoid such risk of unblocking.

Fig. 7 illustrates an embodiment of an analogue multiplierdevice `or the `like wherein two electronic switches according to Fig. 4 are included 'and actuated from .a single control trigger stage. This multiplier is adapted to operate according .to well-known Aprinciples whereby one o f the variable simulating vvoltages lis timefdivided under control of a .rectangular 'waveform 'which has been previously pulse position modulated 'by the other variable simulating Voltage. Consequently the means or 4average component of the waveform final-ly obtained is proportional to the product value yof these two variables.

,I n Fig. 7, 'parts 1 01 and 102 designate vtwo high gain amplifiers of the D.C.` type, each for example consisb in g of three cascade amplification stages. Conventional means may be included to prevent the `drifts 'of Vtheir DzC. supplies. Amplifier 101 -is 'provided 'with a 'capacitive feedback 111 so that it `operates as an electrical integra tor, ,the output of vwhich is always proportional Ato the integral value ,of kits input. Amp'lier 102 Vis similarly provided with v a negative feedback loop and, `according to whether impedance 112 is .resistive or capacitive, it will operate as a mere summing 'amplifier or las a summ ming and integrating amplifier. In the first case, the amplifier will deliver a voltage representing the product of the quantities concerned and in the second case, the integral of this product. s

Input 21 of amplifier "101 receives Ithree voltages from the `following network: 'a first resistor 50, of lhigh impedance value receives from its input terminal 51 the first variable voltage X; a .Second resistor 59 of the same value receives from its input terminal a reference constant potential E0 of a negative polarity; a series attenuator 31-141-41, of an overall value equal to each one of the two resistances '50 and 59, receives from its input terminal 11 la reference voltage of positive polarity and 0f -a Value 22E". aftenatr-ntwk ffr-rnSpa-ltof a first electronic switch of the kind shown in Fig. 4, and is provided with a first diode 6'1 connected point t51 and a second ,diode 261 connectedat .point 151. The anode of diode 26'1'is grounded. The cathode of the first diode is connected by conductor 191 to the cathode of cathode follower tube 21, the biasing resistor 36 of which receives voltage -U1, the plate of which receives potential +U2. The control grid of tube 21 vis biased through resistor 23 and connected by series resistor ,24 to one of the plate outputs of a bistable trigger Istage 25. One of the control grids of trigger stage is Xedly biased, and the other isconnected to the output of amplifier 101 through a suitable voltage divider 121.

When amplifier 101 is at rest, its output potential is high and this ensures the conducting state of the left-hand tube of the ip-op stage 25. The right-hand tube is off; ,cathodeefollower tube 21 conducts and blocking voltage U2 is applied to diode61. When a signal develops across input terminal 51, the output from the ampliier decreases' to such a point that it can no longer counterbalance the negative bias of Vthe left-hand tube of trigger state 25. This vleft-hand vtube is blocked and the right-hand tube is turned on. Cathode follower tube 21 is blocked and voltage .-U1, is applied tothe cathode of diode `61., causing it to'conduct. As --U1 is substantially equal to `#-2139, the negative residual voltage as appearing at point 151 turns on diode 261 so that point 151 substantially assumes ground potential. The signal at 21 which was X .-i-E then becomes X Eu. The output from amplifier 101 increases until the point is reached when the left-hand tube of the ip-op is again lturned on. This turns off the right-hand tube and vblocks `the diodes; and so forth.

Amplifier 102, on the other hand, receives as its input signalv at 22 the combination of the following four input voltages: `--Eo from terminal f52 through ya yligh Value resistor 53: -KLX from terminal 54- through a resistance 55 of the same high value; -l/zY from terminal S6 through a resistor 57 also of this value; and through attenuator network comprising two parallel resistors 32 and 32 and two, serially connected, the resistances 142 and 42, the combined voltage 2E0Y from the respective input terminals 12 and 13. ZBO is a positive potential always higher than the arithmetical Value of the algebraically varying potential iY. The overall resistance of the network is equal to the value of any one of the resistors 53, 55 and 57. At point 52 of this network diode 62 is connected and at point 152, diode 262. The connections of these diodes are substantially identical with those disclosed for the diodes of the 'drst switching arrangement; diodes 62 and 262 are controlled from trigger stage 25 and cathode follower tube 21 substantially simultaneously with diodes 61 and 261 of the rst switch.

Consequently, the value of voltages alternatingly transmitted through the second electronic switch are ZEOY and 06, respectively.

Denoting by the variable voltage iY, by t1 any time interval during which diodes 6 and 26 of both switches are blocked, and by t2 any time interval during which these diodes are conducting, the output signal at 122 will represent the following quantity Denoting by U the amplitude of variation of the output signal from 101, always constant for the actuation of the llip-fiop stage 25, t1 and t2 are given by the following relations:

U (11) tl-E0 X U (lll) Substituting in relation (i), the values of t1 and t2 given by relations (ii) and (iii), then results:

Since corrective voltages Em -l/zY, -KLX are introduced in the input of the amplifier 102 (K1 being an experimentally determined coefficient), the true signal S X .Y V1) 2E0 which is proportional to the product of the two variable quantities X and Y, as required.

It is apparent from further consideration of the electronic switch including attenuator 32-142-42 and diodes 62 and 262 that, notwithstanding an appropriate selection of U1, a fluctuating residual voltage will remain at point 52. This value of U1 must be such that it stands at the midpoint of the range of variation of the signal at 52 and, since Y can vary in both polarities within substantially a wide range, accuracy of switching will dependupon the additional reduction of this uctuation due to the provision in this switch, according to the invention, of a second diode 262. In the first switch, the provision of diode 261 similarly permits reduction of the residual constant voltage which may be of substantial value since U1 is imposed by the second variable Y and not really selected in accordance with X.

Residual voltages with fluctuation reduced by the provision of electronic switches according to the invention may be compensated by opposing voltages in the following way.

From a testpduring which only the three terminals 1 of the arrangement are fed, the values d1 and d2 of these residual voltages are determined at terminals 2 and 22. Then corresponding voltages D1 and D2 are introduced, respectively, at terminals 11 and 13, mixed with the reference voltages applied to these terminals. These voltages are of negative polarities, so they can be denoted by D1 and D2 and their values take into account the attenuations of the resistances through which they will be seen from terminals 21 and 22. In the iirst channel further, a voltage +D1 will also be introduced at 5S. Consequently both voltages D1 and -l-Dl will cancel each other as long as diodes 61 and 261 will be non-conducting. As soon as these diodes conduct, compensation voltage +D1 alone operates to cancel residual voltage d1, as seen at the output of attenuator 3114L4l. In the second channel, a voltage -l-D2/2 will be applied to terminal 52, together with voltage -E0. Further, it will be further noted from the above calculations that voltage -KLX must be modied by the addition of a voltage equal to K1.X.(D2/2E0). This latter voltage may be obtained, as known per se, from the slider of a potentiometer receiving voltage KLX across its terminals and having this slider so adjusted as to impose an attenuation ratio by D2/2E0 to this voltage.

We claim:

1. An electronic switch comprising in combination a series resistance attenuator, means for applying to one end thereof an electric input signal to be derived with a predetermined attenuation at the other end thereof, a diode element having one of its electrodes connected to an intermediate point of said attenuator, at least one further diode element having one of its electrodes connected to a further point of said attenuator which is below the rst in the direction of transmission, and separate means for selectively biasing both diode elements to be substantially simultaneously non-conducting and substantially simultaneously conducting, respectively; the latter means including means for biasing said diode elements differentially so as to reduce the residual voltage at said further diode element with respect to that at the first diode element.

2. An electronic switch according to claim 1 comprising a source of constant voltage connected to compensate said reduced residual iiuctuation, said differential biasing means being adjusted to further reduce said residual lluctuation to such a value as to be substantially cancelled by said compensating voltage irrespective of the possible fluctuations of the residual voltage on either side of an average value.

3. An electronic switch according to claim 1 comprising means for applying to the output end of said attenuator -a constant voltage when the diode elements are conducting, and also for applying to another point of said attenuator another constant voltage of a polarity opposite to that of said rst constant voltage and of such value that said iirst Voltage is substantially cancelled when the diode elements are non-conducting.

4. An electronic switch according to claim 3, wherein said means for applying a constant voltage to the output end of said attenuator include an input terminal to which said voltage is applied, a further series resistance through which it is attenuated, and which has substantially the same value of resistance as said first attenuator, and the other end of which is connected to the output end of said first attenuator.

5. An electronic switch according to claim 1 comprising means for mixing in said attenuator the electric signal to be transmitted with a reference voltage of such value that the resulting voltage always remains of a single predetermined polarity in the path extending from said first diode connection to the output end, and further means for applying to said output end at least part of said reference voltage in such a polarity as at least partially to cancel a portion ofthe output signal corresponding to said reference voltage. i l

6. An electronicswitch according lto claim ,i wherein said attenuator includes a of mixing resistances vccllrnefited rin parallel to said lirst diode connection, com prising means for applying to said VYparallel resistances input signal and reference' voltage respectively.

7. electronic switch according .to claim 5 wherein said means for applying at the output end of the attenuator a constant voltage compensating at least partially said V,reference voltage includes ,an input terminal for 'said constant voltage 'and a series resistance from said input terminal to the output end .of the attenuator, of such a value as to attenuate the input voltage applied from said 'input terminal.

8. An electronic switch according #to lclaim l21 Eto operate upon fluctuating input signals, comprising a biasing terminal for at least one of said diode elements and means for feeding to said biasing terminal an attenuated component of the output voltage of a polarity reversed with respect to that of the input signals of the attenuator.

9. An electronic switch according to claim 8, wherein said feeding means include at least an input terminal for the application thereto of signal voltage of reversed polarity, and an attenuating series resistance extending therefrom to said biasing terminal in parallel with a biasing resistance therefor.

10. An electronic switch according to claim l, wherein at least one of said biasing means includes change-over means for controlling at least the first diode element of the switch from its conducting state to its non-conducting state and conversely.

1l. An electronic switch according to claim 10, wherein all said diode elements include biasing terminals and `are of the same direction between the connecting points of the attenuator and said biasing terminals, and wherein said change-over means control the biasing voltage values for all said diode elements substantially simultaneously.

12. An electronic switch according to claim 10, wherein said first diode element only is controlled from said change-over means and is of a direction opposite to that of any other diode element in said switch said other diode element receiving a constant biasing voltage, and said lirst diode element being so controlled by said change-over means that the residual voltage therefrom, when conducting, insures the corresponding change-over of conditions of the other diode elements of the switch.

13. An electronic switch comprising in combination a series resistance attenuator, means for applying to one end thereof an electric input signal to be derived with a predetermined attenuation at the other end thereof, a diode element havin-g one of its electrodes connected to an intermediate point of said attenuator, means for biasing the diode element to block said signal apart from a residual voltage due to signal uctuation, lat least one further diode element having one of its electrodes con nected to a further point of said attenuator which is below the first in the direction of transmission, and further means for biasing the other electrode of said further diode element in predetermined amplitude relation to said first biasing means to at least Ifurther reduce the residual voltage from the first diode element, at least one of said biasing means including change-over means for controlling at least the iirst diode element of the switch from its conducting state to its non-conducting state and conversely, said change-over means including at least a bistable flip llop stage, and a cathode follower stage having an input controlled from one output of the llip op stage; said cathode follower stage receiving a cathode bias voltage such that, when blocked, the corresponding diode element of the switch is made conducting, and receiving a plate voltage such that, when unblocked, the corresponding diode element of the switch is made non-conducting; there being provided inp-ut means for controlling the ip op stage from one of its conditions to the other.

14. An electronic switch according to claim 13, Wherein 'there are .provided Sas many cath' de follcwcr Stfgc's' aslthcrearcioderclemcnts ln'lthc h, cach yQ21 d? follower ,Stage .being controlled from .Said 'single flip "tldp stage `and each 'bain adapted Eto receive. thcdc plate voltages dctcmuncd'by .the corresponding .dinde ,element to be .controlled thcrcfnlmV '1"5. '1n 4an electronic ,switc' 111s apparatus, .attenuating means including a .Series ,.rcslstcncc'., ihfcaiis fr .appli/11h? a signal to the input end of said 'attenuating means for receiving an attenuatedsignal .the output of said attenuating means, Aa number of diode elements, each of said diode elements Ahaving :one of 'its electrodes connected to one -point along ,said series resistance; the points along 'said series .resistance belingrprede'ternlinedly spaced; biasing means .including lbiasing* terminals connected to the other one of said electrodes, and means for applying to said biasing terminals a corresponding number of biasing voltages substantially simultaneously to transfer the diode elements substantially simultaneously from their conducting states to their non-conducting states and conversely; said biasing voltages in the conducting states of said diodes being adjusted to reduce the residual voltage of at least one of the diodes farther from said input end with respect to the residual voltage of at least one diode closer to said input end.

16. Apparatus according to claim 15, wherein at least part of said biasing voltage applying means is under control of the signal.

17. In an electronic switching apparatus, signal attenuating means forming a series resistance path, means for applying pulse signals at one end of said path, means for receiving attenuated s-ignals at the other end of said path, a number of diode elements having one of their electrode points connected respectively to predetermined points along said series resistance path; and means under control of pulse signals for biasing the other diode electrodes substantially simultaneously; said biasing means including means for transferring the diode elements simultaneously from their conducting states to their non-conducting states and conversely, and means for biasing said elements in their conducting states differentially so as to reduce the residual voltage of at least one diode element farther from the first end of said resistance path with respect to that of at least one diode element closer to said first end of said resistance path.

18. An electronic switch according to claim 17 comprising means under control of pulse signals for applying to the output end of said attenuating means a voltage when the diode elements are conducting, and for applying to another point of said attenuator another voltage of a polarity opposite to that of said irst voltage and of such value that said first voltage is substantially cancelled when the diode elements are non-conducting.

19. An electronic switch according to claim 17 comprising means for mixing in said attenuating means the pulse signals to be transmitted with a reference voltage of such value that the resulting voltage always remains of a single predetermined polarity in the path extending from the rst diode connection to the output end of said attenuating means, and means for applying to said output end at least part of said reference voltage in such a polarity as at least partially to cancel a portion of the output signal corresponding to said reference voltage.

20. An electronic switch according to claim 17 to operate upon fluctuating input signals, wherein said biasing means include a biasing terminal for at least one of said diode elements, and means for feeding to said biasing terminal an attenuated component of the output voltage of a polarity reversed with respect to that of the input signal of the attenuator.

21. An electronic switch according to claim 17. wherein all said diode elements are of the same direction, and said biasing means include change-over means for controlling the biasing voltage values for all said diode elements substantially simultaneously. i

22. An electronic switch according to claim 17, wherein said biasing means include change-over means for controlling the biasing voltage of at least the first diode element of the switch; said rst diode element being of a direction opposite to at least one other diode element in said switch, and being so controlled by said change-over means that the residual voltage therefrom, when conducting, insures the corresponding change-over of conditions of the other diode elements of the switch.

References Cited in the tile of this patent UNITED STATES PATENTS 2,434,929 Holland et al. Ian. 27, 1948 2,535,303 Lewis Dec. 26, 1950 2,548,913 Schreiner et al Apr. 17, 1951 Jacob Jan. 22, 1952 Goldberg Mar. 17, 1953 De Boisblanc Nov. 3, 1953 Harder Dec. 14, 1954 Crayford Jan. 25, 1955 Clayden Jan. 17, 1956 Creusere Nov. 13, 1956 FOREIGN PATENTS Italy Feb. 18, 1936 OTHER REFERENCES An Analogue Multiplier, Nature, January 1951. 15 A Square Root Law Circuit, by I. G. Baxter, March 

